The invention relates generally to multichannel heat exchangers with dissimilar flow across the width of multichannel tubes.
Heat exchangers are used in heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems. Multichannel heat exchangers generally include multichannel tubes for flowing refrigerant through the heat exchanger. Each multichannel tube may contain several individual flow channels, or paths. Fins may be positioned between the tubes to facilitate heat transfer between refrigerant contained within the flow paths and an external fluid passing over the tubes. Moreover, multichannel heat exchangers may be used in small tonnage systems, such as residential systems, or in large tonnage systems, such as industrial chiller systems.
The transfer of heat within multichannel heat exchangers is generally driven by flow of an external fluid passing through the heat exchanger. Typically, as the fluid passes through the heat exchanger (i.e., over the tubes), the fluid contacts the individual multichannel tubes and flows across each tube, contacting first a leading edge of the tube, flowing across the width of the tube, and contacting last a trailing edge of the tube. Heat transfer between the external fluid and the refrigerant is dependent on, among other things, the temperature difference between the external fluid flowing across the multichannel tubes and the refrigerant flowing inside the multichannel tubes. For example, in an evaporator, an external fluid, such as air, may flow over the multichannel tubes. The refrigerant flowing inside the multichannel tubes is generally cooler than the air and, therefore, absorbs heat from the air. The exchange of heat may produce cooled air exiting the heat exchanger and warmed refrigerant flowing within the heat exchanger. In an example employing a condenser, an external fluid, such as air, may flow over multichannel tubes containing a refrigerant that is generally warmer than the air. As the air flows across the tubes, the internal refrigerant transfers heat to the air. The exchange of heat may produce warmed air exiting the heat exchanger and cooled refrigerant flowing within the heat exchanger.
In both evaporator and condenser applications, the greatest temperature difference between the external fluid flowing across the tubes and the internal refrigerant flowing within the tubes generally exists at the leading edge of the tubes. As the external fluid flows across the width of the tubes, heat transfer occurs causing the external fluid temperature to approach the temperature of the internal refrigerant. Therefore, less heat transfer may occur at the trailing edge of the tubes because the external fluid has already absorbed or transferred some heat to or from the internal refrigerant.